1. Field of the Invention
Embodiments of the present invention generally relate to a directional antenna system for portable communication system. More specifically, embodiments of the present invention relate to a directional antenna system, a transmit antenna control circuit, a warning system on the RF receiving signal strength and a transmit antenna user control interface to allow the user to operate the portable communication system in a low electromagnetic energy emission mode and provide an alert when the transmit directional antenna that is pointing towards the user is in operation.
2. Description of the Related Art
Antenna designs employed in the present mobile communication systems are generally using a monopole antenna design. This monopole antenna design provided a 360° operation angle and has good bi-direction RF communication to the transmitter and receiver base towers. The antenna can be in pole shape or in planar shape for compact assembly. As people become more aware of increasing electromagnetic energy exposures from operating mobile communication system, this monopole antenna design exposes the user to the electromagnetic energy due to the 360° antenna operation design.
There is an opportunity to improve the antenna operation to minimize the exposure of the electromagnetic energy to the user as described in the patents by Wang et al., Luxon et al., Jarvis et al. and Kunz on methods in shielding the user from the monopole antenna. The issues in these approaches are lower antenna efficiency in both transmitting and receiving the RF signal as part of the antenna operating angle is limited by the antenna shield. In the patent application by Wong et al., they uses a passive metal shield over their planar antenna system and thus have the similar issues as the patent described above.
Other technique using directional antenna as described in the patent by Dorfman using a 60 degree forward and backward pointing directional antenna. The narrow operating angle allows the user to stay away from the operating electromagnetic energy but the signal quality of the communication device and the reliability usage is also limited because of this narrow operating angle. In the patent described by Underbrink et al. they uses a directional antenna that is pointing away from the user. The communication device has only a partial antenna operating angle and is strongly restricting the user's mobility and this technique also requires base station modification.
Other antenna control technique as described in the patent by Sunaga using a plurality of built-in antennas in the cell phone and select the antenna with the best reception level. The antennas in use are not designed and arranged to minimize the electromagnetic radiation to the user.